This invention relates to a driving shaft including at both the ends yokes constituting parts of respective universal joints and an intermediate slidable portion composed of a male shaft member and a female shaft member fitted with each other by means of splines, and more particularly to a method for producing the driving shaft.
With a driving shaft of this kind, it is often desirable that either the male shaft member or the female shaft member is axially contractible when being subjected to axial stresses causing the driving shaft to be contracted in excess of its predetermined elongation and contraction strokes. For this purpose, it has been proposed that a male or female shaft member is composed of at least two parts which are connected to each other by means of shear pins which may be broken when a predetermined load is applied thereto. It has also been proposed that either a male shaft member or a female shaft member of a driving shaft is connected to an axially contractible tube in order to make it possible for the driving shaft to contract axially when stresses in excess of a predetermined value are axially applied thereto. Moreover, it has been proposed to connect the two parts aforementioned by means of a snap ring, key, spline fitting in metal to metal contact, or adhesive.
With the shear pins described above, the connecting portions for the two parts are located only at two diametrically opposed positions, so that when the pins are progressively fatigued in use for a prolonged period of time, the load to be controlled by the pins would be changed. In other words, the limit of load determined by the pins would become lower than the initially aimed limit of load. With the use of deformable tube, moreover, it would be difficult to control the load at which the tube exhibits its effective performance. Namely, it would be difficult to determine the limit of load at which the tube starts to contract.
It is an object of the invention to provide a driving shaft which eliminates all the disadvantages of the prior art driving shaft and which is able to easily control the load causing the driving shaft to be contracted when being subjected to stresses in excess of a predetermined value.
In order to accomplish this object, the driving shaft according to the invention includes a male shaft member comprising
a) a hollow shaft member having one end connected to said yoke of the universal joint and having an inner surface whose inner diameter is larger than the outer diameter of one end of said female shaft member on the side of said male shaft member, and
b) a splined male member having a splined slidable portion slidably fitted in a splined hole of said female shaft member and a fixing portion to be fitted in said inner surface of said hollow shaft member and further having an elastic body interposed between the inner surface of said hollow shaft member and the outer surface of said fixing portion to fix said splined male member to said hollow shaft member.
With this construction according to the invention, when a contraction in excess of a predetermined value occurs in the splined slidable portion, the female shaft member moves over the splined slidable portion of the splined male member so as to be in contact with the fixing portion of the splined male member with their end faces to urge the splined male member in its axial direction. If such an axial load exceeds the holding force derived from the frictional engagement between the hollow shaft member and the splined male member with the aid of the elastic body between the hollow shaft member and the fixing portion of the splined male member, the splined male member slidably moves in its axial direction relative to the hollow shaft member, whereby the male shaft member entirely contracts or the driving shaft is greatly contracted as a whole.
According to the invention, the axial load acting upon the driving shaft can be controlled by the frictional engagement between the hollow shaft member and the splined male member with the aid of the elastic body therebetween.
In a preferred embodiment, on being subjected to axial displacement and axial load in excess of those in the ranges in normal use, the female shaft member is brought into contact with the fixing portion of the splined male member with their end faces to cause the splined male member to disconnect from the hollow shaft member. In general, for example, with driving shafts for use in automobiles, vehicles for agricultural machineries, industrial vehicles, vehicles for construction equipment and the like, the axial displacement of the driving shaft in use may be 0 to 200 mm, while the axial load may be 0 to 1,000 kg.
In another preferred embodiment, the hollow shaft member is provided in the inner surface with a spline-shaped fixing portion, the fixing portion of the splined male member is formed as a splined fixing portion to be fitted in the spline-shaped fixing portion of the hollow shaft member, and the elastic body being interposed between the spline-shaped fixing portion and the splined fixing portion. If the splined slidable portion and the splined fixing portion are equal in size, it is preferable to form the spline grooves of these portions to be circumferentially shifted from each other with phase difference of one half of the pitch of the spline grooves.
In a further preferred embodiment, the fixing portion of the splined male member is formed as a radially enlarged portion having a diameter larger than the outer diameter of the end of the female shaft member adjacent the splined male member, and the end face of the radially enlarged portion is formed with an annular groove into which the forward end of the female shaft member enters.
In another aspect of the invention, in a method for producing a driving shaft of the kind mentioned in the first paragraph and said male shaft member including a) a hollow shaft member having one end connected to said yoke of the universal joint and having an inner diameter larger than the outer diameter of one end of said female shaft member on the side of said male shaft member, and b) a splined male member having a splined slidable portion slidably fitted in a splined hole of said female shaft member and a fixing portion to be fitted in the inner surface of said hollow shaft member,
the method according to the invention comprises the steps of:
applying a resin coating to either said inner surface of said hollow shaft member or said fixing portion of said splined male member,
inserting and fitting said fixing portion of said splined male member in the inside of said hollow shaft member, and
fixing said hollow shaft member and the splined male member to each other by means of swelling of the resin and/or restoring force due to elasticity of the resin of said resin coating.
According to the method of the invention, the axial load can be controlled by the thickness of the resin coating applied to either the inner surface of the hollow shaft member or the fixing portion of the splined male member and the coated area of the swelling accelerator for swelling the resin coating, for example, the total opening area of the continuous groove or recesses spaced apart from each other provided in the surface of the mating member with which the resin coating is brought into contact.
With this construction, when a large axial load is applied to the driving shaft, the female shaft member moves to be in contact with the fixing portion of the splined male member with their end faces to urge the splined male member in the manner as described above. If such an axial load exceeds the holding force derived from the frictional engagement between the inner surface of the hollow shaft member and the fixing portion of the splined male member with the aid of the resin coating, the splined male member slidably moves in its axial direction relative to the hollow shaft member, whereby the male shaft member entirely contracts or the driving shaft is greatly contracted as a whole.
In a preferred embodiment, the inner surface of the hollow shaft member is formed with a spline-shaped fixing portion, and the fixing portion of the splined male member is formed as a splined fixing portion to be fitted with the spline-shaped fixing portion. With this construction, the relative rotation between the hollow shaft member and the splined male member is prevented in a reliable manner.
In another preferred embodiment, a resin coating is applied to either the inner surface of the hollow shaft member or the fixing portion of the splined male member, and a continuous groove or recesses spaced apart from each other are formed in the opposite circumferential surface of the other not provided with the resin coating and a swelling accelerator for swelling the resin of the resin coating is coated on the groove or recesses. With this construction, the holding force derived from the frictional engagement can be more easily controlled by varying the amounts of the resin coating and the swelling accelerator.
The method according to a further aspect of the invention comprises the steps of:
applying a resin coating to either said inner surface of said hollow shaft member or said fixing portion of said splined male member, and forming a continuous groove or recesses separated from each other in the other not provided with said resin coating,
inserting and fitting said splined male member in said inner surface of said hollow shaft member and thereafter heating said fixing portion to melt said resin coating so as to cause part of the melted resin to flow into said continuous groove or separated recesses and to solidify therein, thereby fixing said splined male member to said hollow shaft member with the aid of the solidified resin, and
slidably fitting said splined slidable portion of said splined male member fixed to said hollow shaft member into said splined hole of said female shaft member by means of splines.
With this construction, when a large axial load is applied to the driving shaft, the female shaft member moves to be in contact with the fixing portion of the splined male member with their end faces to urge the splined male member in the manner as described above. If such an axial load exceeds the restoring force of the resin coating caused by its elasticity between the inner surface of the hollow shaft member and the fixing portion of the splined male member and the shearing force and holding force derived from the frictional engagement by the resin projecting in the continuous groove or separated recesses, the splined male member slidably moves in its axial direction relative to the hollow shaft member, whereby the male shaft member entirely contracts or the driving shaft is greatly contracted as a whole.
According to the method of the invention, the axial load can be controlled by the thickness of the resin coating applied to either the inner surface of the hollow shaft member or the fixing portion of the splined male member and the total area of the continuous groove or recesses spaced apart from each other into which the coated resin flows upon being heated. The resin may be heated by the high-frequency induction heating or by the use of welding heat generated in welding components.